The present invention generally relates to communications systems. More particularly, the present invention relates to a wireless transmission scheme for transmitting images utilizing a cross layer method integrated the slice allocation and multiple modulation and coding modes selection without the need of feedback channel.
Multicast and broadcast services (MBS) such as mobile IPTV are regarded as important applications in WiMAX (Worldwide Interoperability for Microwave Access) networks. It is desirable in a wireless network to simultaneously transmit the same video content to a group of users to reduce bandwidth consumption compared with transmitting the content to each user individually. However, the wireless environment is known to be error-prone because of attenuation, shadowing, multipath fading, interference and mobility of terminals. As a result, the channel characteristics vary in time and location. Even under a connection-oriented network like WiMAX, the reliable transmission and QoS guarantee for MBS is still a challenging task. Compared to unicast service, one difficulty originating in MBS comes from the fact that the channel conditions between the BS(Base Station) and each of the MSs (Mobile Station) in a multicast group may differ and in the absence of feedback, which constrains the performance and deployment of mechanism relying on the channel estimation.
By Using Adaptive Modulation and Coding (AMC) scheme, a WiMAX system can choose a higher order modulation scheme or a lower order modulation scheme. In the area near to the BS when SNR (signal-to-noise ratio) is good, the system can use the higher order modulation scheme to maximize data transfer. In an area close to the cell boundary with poor SNR or in a mobile system subject to multipath or shadowing interference, the system may step down to a lower order modulation scheme to maintain the connection quality and link stability. However, AMC alone is only suitable for unicast service with dedicated feedback channel, there is no direct feedback channel defined for MBS. Thus, the operating condition of individual receivers is unknown to the BS and therefore adjustment on the source side during transmission are unavailable.
There are 3 conventional methods for the MBS in wireless transmission. Taking the coverage with high priority, the first approach chooses the most robust modulation for MBS in order to guarantee the reliable transmission in the whole cell. The disadvantage is the poor performance for spectrum efficiency and the total number of supporting services will be limited. The second trend is to deploy multiple bitstreams of the same source sequence, generated with different parameters set and rate, the receiver can switch from one of them to another based on the channel condition it detects. The shortcoming is the redundancy traffic introduced will cause bandwidth waste. The third one is selecting one group leader to report the channel quality through Channel Quality Information (CQI) channel to the BS as the basis of adjustment, the problem is the group leader can only represent the receivers near to itself, such setting heavily penalizes those terminals exhibiting better or worse channel conditions.
The WiMAX standard supports an adaptive modulation and coding (AMC) scheme that enables throughput optimization based on the propagation conditions. Under the same channel bandwidth, the higher order modulation can achieve higher data rate during transmission, but higher order modulation requires better channel conditions, so it has shorter reliable transmission distance than lower order modulation.
It would be desirable to provide different types of video quality in term of display region for the receivers located under different channel states inside the coverage of BS. A desirable solution to overcome the above stated problems would improve the transmission utility and spectrum efficiency for video MBS service in mobile WiMAX network without the need of feedback channel.